1. Field of the Invention
The present invention relates to a spectrometric measuring instrument using suitable changes in state of polarization of light for application of measurement of a thickness or quality (optical constant, sample structure, etc.) of a thin film, and the like, and particularly relates to a spectrometric measuring instrument suitable for in-line measurement performed in a production line.
2. Description of Related Art
In semiconductor manufacturing processes, recent upsizing, as well as miniaturization of design rules, of semiconductors substrates has raised the possibility of occurrence of excessive damage due to defect possible and necessitated control of delicate abnormality, and thereby testing is increasingly important.
Also in processes for manufacturing FPDs (flat panel displays) typified by an LCD (liquid crystal display) and a PDP (plasma display panel), screen sizes, fineness, and appearance quality are rapidly on the increase with increase in size of glass substrates. Therefore, in order to produce products of high quality in high yield, the importance of testing becomes increasingly high.
Tests of products in the manufacturing process of this kind, especially a film-thickness test, have hitherto been conducted in off-line measurement using a large and expensive spectrometric measuring instrument. This off-line measurement is performed through the following series of procedures. Products are sampled from a manufacturing process, carried to a spectrometric measuring instrument apart from the line, and then subjected to measurement and checking.
In such an off-line measurement, there has been a problem as follows. In the case where a measured result deviates from a control standard, it requires time to feedback that information to be reflected to the process so as to make a correction. Further, as for products not sampled in the manufacturing line, it is not possible to determine whether of not each of the products deviates from the control standard, thereby causing the yield to be lowered.
Therefore, the needs are growing for, for example, incorporating a spectrometric measuring instrument into a film formation process (in-situ) or immediately after the film formation process in a manufacturing line for products, to realize in-line film thickness measurement, in which a total measurement is performed without sampling products from the manufacturing process, so as to improve the product yield.
As a spectrometric measuring instrument applicable to such in-line measurement, it is required to satisfy the following conditions: (1) having an equivalent function to a function of a spectrometric measuring instrument to be used in a conventional film-thickness measurement; (2) being small-sized and capable of high-speed arithmetic processing; and (3) having resistance to later-described distance fluttering and angle fluttering. Additionally, as design rules have recently become finer, an insulating film and the like have become extremely thinner, and thereby testing of a thickness and quality of an ultra-thin film of several nanometers is increasingly important.
In a conventional film-thickness measurement, a thickness-meter of a spectroscopic analysis system or a polarimetry system is mainly used. However, the thickness-meters of those systems are both comprised of a spectroscope using a diffraction grating, and thus have a drawback of causing the instrument to be large-sized and thus be not suitable for the in-line measurement.
Moreover, since only a reflectance as an average value of an S polarized light and a P polarized light is measurable in the thickness-meter of the spectroscopic analysis system, an amount of information is small as compared to the thickness-meter of the polarimetry system typified by an ellipsometer for gathering up the reflectances of the S polarized light and a P polarized light to calculate a film thickness. It is therefore not possible for the thickness-meter of the spectroscopic analysis system to perform accurate measurement.
Further, in the thickness-meter of the spectroscopic analysis system, a reflectance is calculated by obtaining a ratio between an intensity distribution waveform of a wave incident on the sample and an intensity distribution waveform of a wave reflected from the sample. It is therefore necessary to perform another operation for measuring an intensity distribution waveform of an incident wave at the time of film thickness measurement. Consequently, the thickness-meter of the spectroscopic analysis system has a drawback of increasing the measurement time, which is disadvantageous for the in-line measurement.
On the other hand, in the thickness-meter of the polarimetry system, the intensity distribution waveform of the S polarized light and the intensity distribution waveform of the P polarized light are simultaneously measured, and a film thickness is measured based upon this measurement, thereby not requiring another operation for measuring an intensity distribution waveform of an incident wave. Therefore, the thickness-meter of the polarimetry system requires just a short measurement time and can thus be said to be suitable for the in-line measurement.
Further, analyzing film quality (optical constant, sample structure, etc.) of a material requires a spectrum measured in a wide wavelength region. In terms of measuring the film quality, the thickness-meter of the spectroscopic polarimetry system is advantageously used. It is to be noted that “film thickness” mentioned here means a variety of characteristics such as a refractive index, an absorption coefficient, a band structure, and a crystal structure.
FIG. 42 shows a conventional example of a single incident angle spectroscopic ellipsometer for rotating an analyzer as the thickness-meter of the polarimetry system (cf. Japanese Patent Laid-Open No. Hei 6-288835). In this figure, symbol a denotes a light source part, symbol b denotes a polarizer, symbol c denotes a quarter wavelength plate, symbol d denotes a measurement sample, symbol e denotes a rotating analyzer, symbol f denotes an analyzer driving part, symbol g denotes an electronic calculator, symbols h1 to h5 denote optical detectors, and symbol i denotes a diffraction grating.
For convenience of explanation, FIG. 43 shows an example in which the optical detectors h1 to h5 in the single incident angle spectroscopic ellipsometer shown in FIG. 42 have been replaced by a photo-array type detector. In this figure, numeral 101 denotes multi-colored light source, numeral 102 denotes a polarizer, a numeral 103 denotes a retarder, numeral 104 denotes a sample, numeral 105 denotes an analyzer, numeral 106 denotes a condenser lens, numeral 107 denotes a diffraction grating, and numeral 108 denotes a one-dimensional CCD.
As apparent from FIG. 43, light emitted from the multi-colored light source 101 passes through the retarder 102 and the analyzer 103 to be brought into a state of straight-line polarization, which is incident obliquely on the surface of the sample 104. On the optical path of the reflected light from the sample 104, the analyzer 105 for checking the state of polarization, the condenser lens 106, the diffraction grating 107 having a spectral function, and the photo-array detector 108 are arranged in this order. Thereby, the state of polarization of the reflected light with respect to each wavelength is measured to acquire a corresponding spectrum. Finally, an arithmetic part (not shown) performs fitting of a theoretical waveform to a measured waveform, to calculate a film thickness of the sample.
As for the foregoing single incident angle spectroscopic ellipsometer, since it is comprised of a spectrometer using a diffraction grating, the instrument becomes large-sized (first problem), and thus becomes difficult to incorporate the instrument in a line for the in-line measurement.
In the case where later-described distance fluttering occurs, an intensity distribution waveform of reflected light observed does not change. However, in the case where later-described angle fluttering in a horizontal direction or angle fluttering in a perpendicular direction occurs, an intensity distribution waveform of reflected light observed widely varies (second problem), to make measurement difficult. That is, since the single incident angle spectroscopic ellipsometer is susceptible to the distance fluttering as well as the angle fluttering, it is impossible to perform the in-line measurement in terms of actual application of the ellipsometer. For resolving such a situation, a stage needs arranging exclusively for fixing a sample required to be measured, which significantly restricts conditions for setting the instrument.
Further, since it is necessary to position a distance to the sample and inclination of the sample prior to measurement (third problem), it takes time to adjust the stage. This results in an increase in measurement time, and thereby the single incident angle spectroscopic ellipsometer is considered as not appropriate for the in-line measurement.
[Explanation of Distance Fluttering]
“Distance fluttering” is described while referring to FIGS. 44 to 46. In FIGS. 44 to 46, numeral 201 denotes a multi-colored light source, numeral 202 denotes a polarizer, numeral 203 denotes a retarder, numeral 204 denotes a sample such as a semiconductor product or an FDP, numeral 205 denotes an analyzer, numeral 206 denotes a condenser lens having a convergence point on a light-receiving face of a one-dimensional CCD, numeral 207 denotes a diffraction grating, numeral 208 denotes a one-dimensional CCD, and those figures show simplified examples of the invention described in Japanese Patent Laid-Open No. Hei-288835.
It is to be noted that FIG. 44 shows a view of the case where the sample is arranged at a reference height, FIG. 45 shows a view of the case where the sample is arranged at a lowered height, and FIG. 46 shows a view of the case where the sample is arranged at a raised height.
The distance fluttering is a phenomenon that a distance between an optical system (e.g. the retarder 203) and the sample 204 varies. If this distance fluttering occurs, the position of a reflected light intensity distribution waveform observed through the one-dimensional CCD 208 varies although the width thereof in the direction of the array line does not vary. Accordingly, an optical constant of the thin film calculated based upon the intensity distribution waveform is inaccurate.
As apparent from the comparison between FIGS. 44 and 45, since the position of incidence of the reflected light L101 from the sample 204 arranged at the reference height on the diffraction grating 207 differs from that of the reflected light L102 from the sample 204 arranged at the lowered height, while the reflected lights L101 and L102 are in parallel, the reflected light intensity distribution waveform W101 when the sample 204 is arranged at the reference height does not agree with the reflected light intensity distribution waveform W102 when the sample 204 is arranged at the lowered height.
Similarly, as apparent from the comparison between FIGS. 44 and 46, since the position of incidence of the reflected light L101 from the sample 204 arranged at the reference height on the diffraction grating 207 differs from that of the reflected light L103 from the sample 204 arranged at the raised height, while the reflected lights L101 and L103 are in parallel, the reflected light intensity distribution waveform W101 when the sample 204 is arranged at the reference height does not agree with the reflected light intensity distribution waveform W103 when the sample 204 is arranged at the raised height.
[Explanation of Angle Fluttering in Horizontal Direction]
“Angle fluttering in a horizontal direction” is described while referring to FIGS. 47 to 49. In FIGS. 47 to 49, the same components as shown in FIGS. 44 to 46 are provided with the same numerals as in FIGS. 44 to 46, and explanations of those components are omitted.
It is to be noted that FIG. 47 shows a positional relation between the optical system and the sample when the sample is arranged at a reference angle (flat face perpendicular to the incident face), FIG. 48 shows the positional relation when the sample is in the state of slanting to the right (leaning to the right), and FIG. 49 shows the positional relation when the sample is in the state of slanting to the left (leaning to the left).
The angle fluttering in the horizontal direction is a phenomenon that the inclination of the sample 204 varies in a direction rotating around a straight line as a central axis, the line being perpendicular to the incident face. If this angle fluttering in the horizontal direction occurs, the width of a reflected light intensity distribution waveform in the direction of the array line observed through the one-dimensional CCD 208 varies, and thereby, an optical constant of the thin film calculated based upon the intensity distribution waveform is inaccurate.
As apparent from the comparison between FIGS. 47 and 48, the reflected light L201 from the sample 204 when arranged at the reference angle and the reflected light L202 from the sample 204 when arranged at the angle leaning to the right are not in parallel, and the respective angles and positions at which the reflected lights L201 and L202 are incident on the diffraction grating 207 differ. Therefore, the reflected light intensity distribution waveform W201 when the sample 204 is arranged at the reference angle does not agree with the reflected light intensity distribution waveform W202 when the sample 204 is arranged at the angle leaning to the right.
Similarly, as apparent from the comparison between FIGS. 47 and 49, the reflected light L201 from the sample 204 when arranged at the reference angle and the reflected light L203 from the sample 204 when arranged at the angle leaning to the left are not in parallel, and the respective angles and positions at which the reflected lights L201 and L203 are incident on the diffraction grating 207 differ. Therefore, the reflected light intensity distribution waveform W201 when the sample 204 is arranged at the reference angle does not agree with the reflected light intensity distribution waveform W203 when the sample 204 is arranged at the angle leaning to the left.
[Explanation of Angle Fluttering in Perpendicular Direction]
“Angle fluttering in a perpendicular direction” is described while referring to FIGS. 50 to 52. In FIGS. 50 to 52, the same components as shown in FIGS. 44 to 46 are provided with the same numerals as in FIGS. 44 to 46, and explanations of those components are omitted.
It is to be noted that FIG. 50 shows a positional relation between the optical system and the sample when the sample is arranged at a reference angle (flat face perpendicular to the incident face), FIG. 51 shows the positional relation when the sample is in the state of slanting backward (leaning backward), and FIG. 52 shows the positional relation when the sample is in the state of slanting backward (leaning backward).
The angle fluttering in the perpendicular direction is a phenomenon that inclination of a sample varies in a direction rotating around a straight line as a central axis, the line being an intersection between an incident face and a face to be measured. If this angle fluttering in the perpendicular direction occurs, the stretching direction of the light diffracted on the diffraction grating 207 is displaced from the array line direction of the one-dimensional CCD 208, whereby the reflected light intensity distribution cannot be completely received on the one-dimensional CCD 208. As a result, an optical constant of the thin film calculated based upon the intensity distribution waveform is inaccurate.
As apparent from the comparison between FIGS. 50 and 51, the reflected light L301 from the sample 204 when arranged at the reference angle and the reflected light L302 from the sample 204 when arranged at the angle leaning backward are not in parallel, and the respective angles and positions at which the reflected lights L301 and L302 are incident on the diffraction grating 207 differ. Therefore, the reflected light intensity distribution waveform W301 when the sample 204 is arranged at the reference angle does not agree with the reflected light intensity distribution waveform W302 when the sample 204 is arranged at the angle leaning backward.
Similarly, as apparent from the comparison between FIGS. 50 and 52, the reflected light L301 from the sample 204 when arranged at the reference angle and the reflected light L303 from the sample 204 when arranged at the angle leaning backward are not in parallel, and the respective angles and positions at which the reflected lights L301 and L303 are incident on the diffraction grating 207 differ. Therefore, the reflected light intensity distribution waveform W301 when the sample 204 is arranged at the reference angle does not agree with the reflected light intensity distribution waveform W303 when the sample 204 is arranged at the angle leaning backward.
It is to be noted that, hereinafter, the angle fluttering in the horizontal direction and the angle fluttering in the perpendicular direction are collectively referred to as the angle fluttering.